Tunable coupled cavity extended interaction electronic tube having deformable end wall



United States Patent 3,379,922 TUNABLE COUPLED CAVITY EXTENDED ENTER- ACTION ELECTRONHI TUBE HAVING DEFORM- ABLE END WALL Walter R. Day, .lr., and Lars H. Sandstrorn, Gainesviile, Fla, assignors to Sperry Rand Corporation, Great Neck, N .Y., a corporation of Delaware Filed Apr. 7, 1965, Ser. No. 446,194 7 Claims. (Cl. SIS-5.38)

ABSTRACT OF THE DISCLGSURE An extended interaction type of electron tube in which the entire interaction circuit structure comprised of aperture-d discs closely spaced to form a series of closely coupled cavities along the beam axis is tunable by deforming the end disc terminating the circuit nearest to the collector.

This invention relates to an electronic tube of the type for generating or amplifying microwave energy, for example, and more particularly the invention relates to an extended interaction type of tube and to the means for frequency tuning the tube.

Extended interaction types of electronic tubes employing an electromagnetic wave circuit comprised of a succession of perhaps ten or twelve directly coupled cavities has stimulated interest because the tube may be operated at higher eficiencies than comparable klystron oscillator and amplifier tubes, for example, and because the tube is broader in its operating frequency band. The coupled cavity extended interaction circuit with which the present invention is concerned is comprised of a plurality of relatively closely spaced conductive discs that are aligned along an axis with the planar surfaces of the discs perpendicular to the axis. Two successive discs form one cavity and three successive discs form two adjacent cavities. Each disc has a central aperture through which the electron beam passes, and each disc, excepting the end discs has a second off-axis aperture that provides direct electromagnetic wave coupling between adjacent cavities. In an oscillator embodiment of the tube, one end disc acts as a short circuit to electromagnetic waves and the other end disc is apertured to provide w-ave coupling .to a section of waveguide that functions as an output connection for the tube. Usually, but not always, the coupling apertures of successive discs are positioned 180 with respect to each other. Because the conductive discs are closely spaced the electric field in each cavity extends axially between the discs and is in wave coupling relationship with the axially directed electron beam. The last one of the cavities is short-circuited to the electromagnetic waves, and together the plurality of directly coupled cavities exhibits a given overall frequency response characteristic. This frequency response characteristic of the coupled cavities, and thus the operating frequency of the tube, are a function of the physical geometry of the cavities. Extended interaction structures of the type under consideration are described and analyzed in an article entitled Propagation Characteristics of Slow-Wave Structures Derived From Coupled Resonators, by E. Belohoubek, published in the RCA Review, June 1958, pages 283-310.

In known coupled cavity extended interaction tubes constructed in the past, either no means at all has been provided for tuning the frequency of operation of the tube, or each of the individual cavities was tuned by inserting an object through a side wall of the cavity, or by having the sidewalls of each of the cavities made of a flexible or deformable conductive material. These tuning means, however, are not practical or feasible in tubes intended to operate in the upper regions of the X-baud and the K-band of the microwave frequency spectrum because the extended interaction type of cavities in these tubes are too small to permit these types of physical arrangements.

In accordance with the illustrated embodiment of the present invention an extended interaction structure that is comprised of twelve directly coupled cavities is cent-rally traversed by an electron beam. The end cavity nearest the beam collector electrode is short-circuited to electromagnetic waves by a deformable conductive end wall and the end wall has a central aperture to permit the electron beam to pass therethrough. The parameters of the electron beam are adjusted so that energy is exchanged from a negative energy beam wave to a circuit wave and oscillations are set up in the coupled cavities. The collector electrode has a central bore therein to collect the beam and is secured by a tubular nib to the central region of the deformable end wall of the last cavity. The collector is cylindrical in shape and extends beyond the end of the main body portion of the tube and is movable axially with respect to the tube body. A rigid rim protrudes outwardly from the cylindrical surface of the collector and the portion of the collector that extends axially beyond the rim is threaded to receive a locking nut. A tuning nut threadably engages the end of the body member and the outermost end of the tuning nut has a radially inwardly extending portion that fits between, and is in a rotatable contact with a shoulder on the rim of the collector and with a face of the locking nut. The tuning nut therefore may be rotated to cause the collector, and thus the deformable cavity end Wall attached thereto, to move axially in either direction, depending on the direction of rotation of the tuning nut. The movement of the end wall of the end cavity changes the overall frequency response of the twelve tightly coupled cavities and changes the oscillating frequency of the tube. This two-way tuning means for the extended interaction circuit of the tube provides means for achieving sufiicient changes in the operating frequency of the tube to make it possible to relax the tolerances on the physical dimensions of the very small component parts of the tube, thereby making a tube constructed in accordance with the teachings of this invention more versatile in its use, less expensive, and easier to manufacture.

The invention will be described by referring to the accompanying drawings wherein:

FIG. 1 is a sectional view of a tunable coupled cavity extended interaction oscillator tube constructed in ac cordance with the teachings of this invention; and

FIG. 2 is a plan view of one of the component members of the tube that make up the successively positioned directly coupled cavities.

Referring now in detail to FIG. 1, a solid electron beam is produced at the left end of the tube by means of a conventional electron gun 10 and a centrally apertured accelerating anode 11. Anode 11 forms a portion of the bottom broad wall of a section of uniconductor rectangular waveguide 13 within which is disposed a stepped impedance transformer 14 which is made of conductive material and which has an aperture 15 therein to permit the passage of the electron beam along the axis. A conventional coupling flange 17 is secured to the outer end of waveguide section 13 and a dielectric waveguide window 18 and a holding frame 19 seal the interior of the tube against the exterior atmosphere.

A collector electrode 21 is disposed at the right end of the tube and is threaded at its outermost end to receive the cooling block 22 having the heat radiating fins 23 thereon.

To the right of waveguide section 13 is the cylindrical shell 25 whose left end forms part of the broad wall of waveguide section 13, and which encloses the extended interaction structure of the tube. This extended interaction structure of the tube is comprised of the aligned discs 26-37 which are made of a conductive material such as copper and which are secured together, as by brazing, so as to form a unitary structure of twelve resonant cavities. All of the discs 2637 are substantially identical and have the shape illustrated in FIG. 2 wherein the disc is illustrated as having the central aperture 46 for the passage of the electron beam therethrough and the off-axis aperture 41 through which the electromagnetic waves couple from one cavity to the next adjacent cavity. A circular ridge 42 of increased thickness extends around the outer periphery of the disc, and when assembled as shown in FIG. 1, is in abutting contact with the adjacent discs. The notches, 43, 44, and 45 on the periphery of the disc are employed to align the discs in their desired positions for final assembly and brazing. As may be seen in FIG. 1, two adjacent discs form one cavity, and three adjacent discs form two cavities, the intermediate disc being common to both cavities and the aperture 41 in that intermediate disc providing the direct electromagnetic wave coupling between the adjacent cavities.

The right end of the direct and tightly coupled cavities is short-circuited to the electromagnetic waves by the deformable end wall 48 of a conductive material which is centrally apertured to permit the passage of the electron beam therethrough. The succession of coupled cavities that are short-circuited by the deformable end wall 48 have a frequency response characteristic that is determined by the geometry and arrangement of the cavity discs 2637. The oscillatory waves are coupled through the coupling aperture 41 in the disc 26 and into waveguide section 13. A microwave circuit of this type possesses a number of discrete resonant frequencies given by the number of half-wavelengths it between the end walls of the structure, or

where {i is the propagation factor of the fundamental component of the wave on the circuit, 1 is the length of the circuit, and n is an integer. For a circuit of m cavities there are m+1 resonant frequencies. When the velocity of the electron beam is made slightly greater than the circuit phase velocity associated with a particular resonance, energy is transferred from the slow space-charge wave on the beam to the wave on the circuit. Oscillation takes place when the negative electron beam conductance is made equal to or greater than the loaded circuit conductance.

Surrounding the collector electrode 21 is the cup-shaped collector shell 52 which has a short tubular nib 53 at its left end, this nib 53 being secured to deformable end wall 48 and having a central aperture 54 in registration with the central apertures in end wall 48 and collector electrode 21. Collector shell 52 has a set of threads 56 about the exterior of its right end and has a protruding rim 57 positioned just to the left of the threads 56. Collector electrode 21 and collector shell 52 are secured together as by brazing so that no relative motion is possible between them. A body member 60 is positioned about cylindrical shell 25 and about a portion of collector shell 52. Body member 60 has a set of threads 61 cut into its exterior surface at its right end.

A tuning nut 64 threadably engages the threads 61 on body member 60 and has a radially protruding cap portion 65 which is adapted to make a butting and rotatable contact with the right shoulder of the protruding rim 57 on collector shell 52. A first locking nut 68 engages the threads 56 on the collector shell 52 and the left face of the locking nut is adapted to make a butting and rotatable contact with the right end face of the cap 65 of tuning nut 64. A second locking nut 69 threadably engages the set of threads 61 on body member 60 and is adapted to make a firm butting contact against the left end surface of tuning nut 64. The cylindrical outer surface on the left end of collector cup 52 is in close but slidable contact with the interior cylindrical surface at the right end of body member 60. It may be seen that the right end of collector member 21 must be of reduced diameter and the cooling block 22 must be threaded thereon in order that tuning nut 64 and the locking nuts 68 and 69 may be inserted over the end of the collector during assembly of the tube.

The frequency of oscillation of the tube may be varied over at least a small range of frequencies that may be necessary to achieve the design objectives for the tube by varying the axial position of deformable wall 48, which effects a volume tuning of the last cavity that is formed by the disc 37 and deformable end Wall 48. Because of the tight coupling between the cavities, a slight tuning of one cavity of the twelve will affect the overall frequency response of the extended interaction circuit so that in practice only one cavity out of the twelve cavities need be tuned to change the frequency of oscillation of the tube. Assuming that it is desired to lower the frequency of oscillation of the tube, the deformable end wall 48 would have to be deformed outwardly toward the right so as to increase the inductance of the last cavity. This may be accomplished in the following manner.

Initially, the first locking nut 68 is backed off a fraction of a turn just enough to permit tuning nut 64 to turn against it. Then locking nut 68 is held against turning and tuning nut 64 is rotated in a direction to advance it to the right. As tuning nut 64 moves to the right its end cap rotates with respect to the fixed locking nut 63 and pushes nut 68 to the right. Because locking nut 68 is now fixed relative to collector shell 52 through their respective threads, the collector will move to the right with locking nut 63 and the nib 53 will pull the deformable end wall 48 to the right. After the desired frequency of oscillation has been achieved, the tuning nut 64 will be held against rotation and the second locking nut 69 will be brought into firm contact with the left end of tuning nut 64, to provide a locking action. Because of some play between the various threads, locking nut 69 should be able to assure that tuning nut 64 and locking nut 63 are in firm contact. If not, locking nut 68 may be turned in against tuning nut 64.

For moving deformable end wall 48 inwardly to the left, locking nut 69 first is moved to the left and out of engagement with tuning nut 64. Then tuning nut 64 is rotated to move it to the left so that its end cap 65 forces against the rim 57 on collector shell 52 and moves the collector and the deformable wall 48 to the left. After the desired operating frequency has been arrived at, the tuning screw 64 is held against rotation while the locking nuts 63 and 69 are brought into firm contact with the two ends of the locking nut 64.

It now may be seen that relatively simple means are provided for varying the frequency of operation of this coupled cavity extended interaction oscillator tube and this means is readily adaptable for use in the very small oscillators and amplifiers that are built to operate in the upper regions of the X and K-bands of the microwave frequency spectrum. It further may be seen that regardless of which direction the deformable wall 48 is to be moved, there is always positive control over the movement of the wall. Therefore, this tuner may be used for the two-way movement of both flexible and deformable walls.

Although the device illustrated in FIG. 1 is an oscillator tube, the same deformable end wall tuning means also may be adapted for use in a coupled cavity extended interaction amplifier.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

We claim:

1. A frequency tunable coupler cavity extended interaction electronic tube comprising in combination,

a tube body having disposed therein a cathode for producing and directing an electron beam axially of said tube, and a plurality of thin conductive members extending laterally of the tube axis and each having a central aperture for the passage of said beam therethrough, said members being secured together in relative spaced relation to form cavities, with their central apertures in alignment and each member having a second aperture for the close coupling of electromagnetic waves therebetween,

the peripheral edge zones of said cavities being connected together by conductive closure means to form an extended interaction type electromagnetic wave circuit structure,

a centrally apertured thin conductive end Wall member forming the cavity end wall farthest from said cathode and being conductively connected at its peripheral edge portion with the other members to form the end of said circuit structure, said last member being deformable in a central zone thereof,

and screw threaded tuning means cooperable with the tube body and including an element secured to said deformable end wall member in a zone adjacent and surrounding the central aperture therein for imparting an axially directed force in either direction to said deformable wall member to effect deformation thereof whereby the operating frequency of the entire circuit structure will be adjusted through operation of said tuning means and the resultant deformation of said last wall member.

2. A frequency tunable coupled cavity extended interaction electronic tube comprising in combination,

a tube body having disposed therein a cathode for producing and directing an electron beam axially of said tube, and a plurality of thin conductive members extending laterally of the tube axis and each having a central aperture for the passage of said beam therethrough, said members being secured together in relative spaced relation to form cavities, with their central apertures in alignment and each member having a second aperture for the close coupling of electromagnetic waves therebetween,

the peripheral edge zones of said cavities being connected together by conductive closure means to form an extended interaction type electromagnetic wave circuit structure,

a centrally apertured thin conductive end wall member forming the cavity end wall farthest from said cathode and being condnctively connected at its peripheral edge portion with the other members to form the end of said circuit structure, said last member being deformable in a central zone thereof,

and tuning means including a centrally recessed driven element and driving means therefor, said driven element being secured to said deformable end wall member in vacuum sealing relation with the recess therein aligned with the central aperture of the deformable end wall member to form a collector and said driven element being supported for axial movement relative to the tube body, and said driving means being mounted for screw threaded engagement with said tube body and for frictional engagement with said driven element to effect axial movement of the driven element in either direction with resultant deformation of said deformable end wall member to thereby adjust the operating frequency of the entire circuit structure.

3. In a tunable electron beam tube in which an axially extending electron beam traverses a body portion that includes a wave supporting structure extending axially of the tube body and having a movable end wall that extends transversely to the beam, the combination comprising a driven tuner element and collector electrode secured together and secured to said movable end wall and a driving tuner element, said driven tuner element extending axially with freedom of movement within the tube body and being formed with a first peripherally extending shoulder spaced from the free end thereof,

removable means adapted to be applied over the free end of the driven tuner element and secured in p0sition thereon to form a second peripherally extending shoulder axially spaced from the first shoulder, and

said driving tuner element being provided with screw threads engageable with screw threads on the tube body to provide axial movement thereof when rotated and said driving tuner element being provided with a lip portion extending into the space between the first and second shoulders of the driven tuner element so as frictionally to engage one or the other of said shoulders and impart axial movement to the movable end wall when said driving tuner element is rotated.

4. A frequency-tunable coupled cavity extended interaction electronic tube comprising the combination,

means for forming and directing a stream of charged particles along an axis that traverses a body portion of the tube,

a plurality of successively positioned directly coupled resonant cavities disposed along said axis in wave coupling relationship with said stream of charged particles,

the cavity positioned last in the direction of flow of said stream having a deformable end wall,

a non-deformable movable member secured to said movable wall and at least a portion of the movable member extending beyond one end of the body portion,

means on said movable member beyond the body portion for forming a shoulder that faces in a direction away from the movable end wall,

a tuning nut threadably engaging the one end of the body portion and frictionally engaging the shoulder means on the movable member,

a locking nut threadably engaging the movable member along its outwardly extending end beyond the shoulder means and engagin said tuning nut in a butting contact, whereby when said tuning nut is rotated in one direction it frictionally engages said shoulder to exert an axial force on said movable member and when rotated in the opposite direction it will frictionally engage said locking nut to exert an axial force on said movable member in the opposite direction to thereby provide two-way movement of the deformable end wall.

5. The combination claimed in claim 4 wherein said non-deformable movable member comprises a collector electrode for the tube,

said collector electrode being threaded at its outermost end, and

a cooling member having a plurality of cooling fins thereon threadably engaging said collector electrode.

6. In a tunable electron beam tube in which an axially extending electron beam traverses a body portion that includes a wave supporting structure having a movable end wall that extends transversely to the beam, the combination comprising a movable member disposed coaxially about said beam and secured to said end wall,

said body portion terminating axially beyond the end wall in a first threaded end section and said movable member extending beyond the body portion and terminating in a second threaded end section,

an outwardly protruding rim on said movable member an outwardly protruding rim on said movable member located in an axial region intermediate the two located in an axial region intermediate the two threaded end sections, threaded end sections,

a first nut engaging said second threaded end section, afirst nut engaging said second threaded end section,

a tuning nut engaging said first threaded end section 5 a tuning nut engaging said first threaded end section and having a cap thereon which is disposed between and having a cap thereon which is disposed between and adapted to rotate with respect to said rim and and adapted to rotate with respect to said rim and said first nut thereby to exert an axial thrust against said first nut thereby to exert an axial thrust against the rim or the first nut depending o th direction the rim or the first nut depending on the direction of of rotation of the tuning nut. 10 rotation of the tuning nut.

7. In a tunable electron beam tube in which an axially extending electron beam traverses a body portion that References Cited includes a wave supporting structure having a movable UNIT STATES PATENTS cbiiirtliagsrlll (tgitperiitstinfs transversely to the beam, the com- 1: 29241738 2/1960 Chodomw 3,060,342 10/1962 Van Der Voorn et a].

a non-deformable movable member secured to said end wall, 3155.54X

said body portion terminating at one end in a first 3167968 2/1965 Sandslmm 3155'48 X threaded end section and said movable member ex- HERMAN KARL SAALBACH Primmy Emminer tending beyond the body portion and terminating H0 in a second threaded end section, PAUL GENSLER, Examine"- 

